U.S. Pat. No. 4,878,518 discloses a fuel delivery system for internal combustion engines that comprises a canister for positioning within a fuel tank. The canister has a lower end with a fuel opening and an internal wall spaced from such lower end dividing the canister into upper and lower fuel chambers. An electric-motor fuel pump is positioned within the upper chamber and has a fuel inlet, a primary fuel outlet for feeding high-volume fuel under pressure to an engine, and a secondary fuel outlet for supplying fuel under pressure at smaller volume than the primary outlet. A fluid conduit extends through the canister internal wall, and has an inlet end in the lower chamber and an outlet end positioned in the upper chamber. A nozzle couples the secondary pump outlet to the conduit for aspirating fuel through the conduit from the lower chamber to the upper chamber. Thus, any vapor collected in the lower chamber is entrained in aspirated fuel and fed to the upper chamber, where it is free to vent to the fuel tank through the open upper end of the canister.
Although fuel delivery systems of the type disclosed in the noted patent have enjoyed acceptance and success, further improvements remain desirable. For example, one acceptance test that is particularly difficult for conventional fuel delivery systems is the so-called priming condition test in which the fuel canister and tank are allowed to run dry, and the tank is then filled with a small quantity such as one gallon of fuel. When it is then attempted to start the engine, the pump is required to purge air and fuel vapor from within itself, draw fuel from the relatively low level in the surrounding tank, and prime itself for delivery of fuel under pressure to start the engine. It is a general object of the present invention to provide a fuel delivery system, and particularly an in-tank fuel module of the type disclosed in the above-noted patent, that possesses enhanced capability for purging air and vapor, and priming itself, when fuel in the surrounding tank is at a low level.